Electrochemical toxic gas sensors, in one form, are designed to be maintenance free and stable for long periods. They have a direct response to volume concentration of gas rather than partial pressure. The simplest form of electrochemical toxic gas sensor comprises two electrodes, a sensing electrode and a counter electrode separated by a thin layer of electrolyte. This structure is enclosed in a plastic housing that has a small capillary to allow gas entry to the sensing electrode and includes pins which are electrically attached to both electrodes and allow easy external interface. These pins may be connected to a simple resistor circuit that allows a voltage drop resulting from any current flow to be measured. Gas diffusing into the sensor is either oxidized or reduced at the sensing electrode and, coupled with a corresponding counter reaction at the other electrode, a current is generated through the external circuit. Since the rate of gas entering into the sensor is controlled by the capillary diffusion barrier, the current generated is proportional to the concentration of gas present outside the sensor and gives a direct measure of the toxic gas present.
One known carbon monoxide sensor suffers from a high or variable level of hydrogen cross sensitivity which can be an issue. A large variation has been observed, depending on catalyst batches used. Such a known sensor consists of a sensing electrode made from normal platinum and a counter electrode made from high surface area platinum and higher and weight of platinum. Two different catalysts were used to ensure that there was enough stability of potential and the like to last throughout the life of the product. Because the catalysts were not exactly matched there can be subtle but important differences in their behavior within the sensor environment.
The present disclosure is directed to improvements in cross sensitivity in a gas sensor.